Mark Udall, left, and Michael Bennet at a rally in Boulder, Colo., this month. As leader of the Democratic Senatorial Campaign Committee, Mr. Bennet works to preserve his party’s majority.CreditMatthew Staver for The New York Times

ENGLEWOOD, Colo. — Dressed alike in bluejeans and light blue shirts, Michael Bennet and Mark Udall, this state’s two Democratic senators, worked a room full of excited volunteers gathered in a campaign office just outside Denver. The idea was to stoke their enthusiasm for a final door-to-door push behind Mr. Udall’s endangered re-election bid.

“He’s all in,” declared Mr. Udall about Mr. Bennet, his junior colleague, who, as the chairman of the Democratic Senatorial Campaign Committee and the man charged with preserving his party’s majority, has almost as much on the line as Mr. Udall.

Mr. Bennet is not only overseeing Democratic efforts in tough Senate races around the country in a political environment tilted against his party, he is also trying to save a seat in his own backyard, where a loss would sting doubly if it helped cost Democrats the Senate.

“After the election is over and if somehow we haven’t held the Senate no matter all the conditions against us and they want to put me in the loser column, the fact that we would have lost Colorado would only add to that designation,” Mr. Bennet conceded. “But I don’t think it is going to happen.”

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Senator Jerry Moran, Republican of Kansas, in a parade in McPherson, in May. Like Mr. Bennet, he has a crucial midterm race in his home state and leads his party’s campaign committee.CreditSandra J. Milburn/The Hutchinson News, via Associated Press

Remarkably, Mr. Bennet is not the only one in such circumstances. His counterpart at the National Republican Senatorial Committee, Senator Jerry Moran of Kansas, also has a crucial race in his home state. A failure by the veteran Senator Pat Roberts to hold his seat there could conceivably cost Republicans the Senate majority so tantalizingly within reach — and leave Mr. Moran on the wrong end of a home-state outcome.

“I expect him to win and would certainly be greatly disappointed if that is not what transpires,” said Mr. Moran, who like Mr. Bennet has been campaigning with his more senior Senate partner.

Presiding over one of the four congressional campaign committees — the House has two as well — can be rewarding and can vault a lawmaker into the leadership ranks if a successful year leads to gratitude and loyalty from re-elected senators and representatives. It can also be exhausting and thankless and leave committee leaders absorbing blame for things over which they have little control — wayward candidates who veer off message, calamitous world events, presidential numbers that spiral down and opposition party candidates who mount surprisingly good challenges.

Leaders of the committees sometimes have to be cajoled into taking the posts. They traditionally are picked because they are ambitious, savvy and not up for re-election. Their states are usually considered safe territory, allowing them to travel the country to court donors and advise contenders.

Nathan L. Gonzales of the Rothenberg Political Report researched the subject and found that no leader of the Republican Senate committee has lost a home state race since 1972 — Colorado coincidentally — and no Democrat ever has.

“We would have to call it a historic loss for either chairman to lose,” Mr. Gonzales said. “For both of them to lose would be unprecedented.”

At the start of 2014, Mr. Moran and Mr. Bennet had little reason to expect trouble in their own states. Mr. Udall was anticipating a manageable rematch in Colorado against Ken Buck, the conservative Republican narrowly defeated by Mr. Bennet four years ago. And in Kansas, the idea of Mr. Roberts, a Republican fixture in Congress, running into serious trouble seemed far-fetched.

But now Mr. Udall finds himself locked in a tight battle with Representative Cory Gardner, the Republican challenger. Mr. Roberts came under siege from the right, the left and the middle, and now faces an independent, Greg Orman, a businessman, in a close race.

The two chairmen have some built-in advantages in helping to protect their home turf. Who knows better how to win Senate races in Colorado and Kansas than the two men who won them most recently?

Mr. Bennet was courted for the job by the Democratic leadership of the Senate because he is a personable, rising Democratic star. He also developed the know-how in 2010 to win a race he was expected to lose, drawing up a template that was used for President Obama’s 2012 victory in Colorado and Mr. Udall’s race this year. The formula calls for hitting the Republican opponent on issues that expand the gender gap to attract suburban female voters. It also emphasizes Democratic appeal to Hispanics, and it puts in place a ground game that can turn out less-motivated voters.

“We know how to do this, and I think we are going to be able to win,” said Mr. Bennet, who will be focusing his personal efforts in the final days on the Colorado race.

Republicans and some other critics have suggested that Democrats adopted Mr. Bennet’s approach too closely in Colorado this year, overemphasizing women’s issues to the point of diminishing returns.

Mr. Moran, who has been assisted in Senate Republican fund-raising chores by Senator Rob Portman of Ohio, took on the job in 2013 after Republicans had just lost Senate seats and were beaten down. He was seen as an unconventional choice given his lack of national political stature and a low-key demeanor.

But Mr. Moran said he had decided to pursue the job after experiencing the dysfunction of the Senate, where he found that as a junior member of the minority he did not have much clout to get anything done. He saw a leadership change as the only solution. And although he did not anticipate having to help rescue Mr. Roberts in Kansas, he figures he is well suited to the job.

“The fact is, the Senate, in my view, is doing nothing,” Mr. Moran said. “It is a story that I certainly have the ability to tell to Kansans. And it is a story I can tell with sincerity across our state.”

A version of this article appears in print on , on Page A19 of the New York edition with the headline: A Role in Steering Midterms: Savior or Scapegoat. Order Reprints | Today’s Paper | Subscribe